Ah, but shapeshifting.... could you do it to such a degree that you shapeshift your arteries healthy and your fat away? Or if there is conservation of mass, shapeshift 20 pounds of flab off your thighs and into your hair, then go for a haircut :D

Hopefully the former since then I could do something drastic like shapeshift into a kid to abuse those all kids enter for free deals, or into an elderly person to abuse social security or senior's discounts, or into a bird if I want to fly over traffic, or even into a gorilla if I just want to go apeshit and ruin somebody's day.

The most amusing thing about shapeshifting powers is that of all the powers out there, it's one of the most underrated in comics. The best use I've ever seen shapeshifting powers used for was in Disney's Sword in the Stone where Merlin changes into a disease to beat a dragon and win a wizard's duel. Now imagine shapeshifting into something like AIDS. Not only can you renew yourself indefinitely, but having the means to immediately and completely fuck somebody over with nothing to stop you save for your own moral compass and rarely some kind of super immunity to illness? Yeah, shapeshifting is horribly underrated.

But as a supervillain, it's far more evil to subjugate a person to a lifetime of torture and ruined existence than to outright kill them. Plus, once cancer cells and all start multiplying, the disease villain can just sneeze himself out and infect his next victim. Or if you're a parasitic worm, just lay a hundred eggs, poop yourself out of your host, and go infect someone else.

Yeah, being able to transmutate into a disease or a parasite is one frightening superpower. Any superhero would have a rough time against a villain who can do that.

Despite all the cool powers people have spoken of, I still stick with wanting the power to be in several different places at once.

Transforming into AIDS? Wouldn't that be a kind of a slow, lingering death. You would be in there for quite a while. I hope you like the taste of white blood cells. :P

Based upon the example I cited I would assume that once you infect a person your work there is done. Hell, in the scene right after the duel you see Merlin standing over his bedridden opponent's bed punching holes in her roof and telling her that it's the only way she'll beat the flu he gave her.

Of course, if you want hang out in a body you could opt to seize control of it. Like one of those Ghould parasites from Stargate.

Amusingly enough though, this very train of thought is the exact reason why Batman should never be allowed to wield a Green Lantern ring. The Caped Crusader of contingency plans and out of the box thinking getting his hands on something that makes semi-real objects based upon the imagination would very much pwn everybody's shit if he felt like it. (How many Green Lantern Corps members had the idea to conjure a Phantom Zone projector out of their rings and just banish whatever it is that's being naughty and villainous in their sights?)